Effects of an internal thermocouple on the response of measured initial LOFT fuel centerline temperatures

The SPC fuel thermal-mechanical analysis code RODEX3 was applied to analyze the temperature response of fuel rods with standard solid pellets and fuel rods with annular pellets which contain an internal thermocouple, for the LOFT L2-5 and L2-6 large-break loss-of-coolant experiments. The analysis was performed to investigate the intrusive effect of an internal thermocouple on the response of LOFT fuel centerline temperatures by comparing measured data with the calculated temperatures of two fuel rods modeled as solid and annular pellets. The analysis results demonstrated that the intrusive effect of the internal thermocouple on the measured fuel centerline temperature is significant. Since the difference between the calculated solid and annular pellet centerline temperatures is large, the measured centerline temperature is actually an indication of the temperature of the inner surface temperature of the annular pellet. The solid pellet centerline temperature calculated to be is significantly greater than the temperature measured by an internal thermocouple. (author)